Conventional deposition methods especially thin layer deposition methods such as vapor deposition, sputtering or PECVD (plasma-enhanced chemical vapor deposition) are used in the production of microacoustic components to produce layers and electrodes. Fluctuations in the thickness of the deposited layer occur in this case. A non-uniform material distribution can occur between different wafers, but also on the same wafer. Since characteristic variables of the components, for example the frequency, are sensitively dependent on the layer thickness, the narrow specifications required are fulfilled only by a small proportion of the components thus produced, unless further complicated process steps are carried out.
If dielectric layers are deposited by one of the methods mentioned, the deposition rate is generally so low that the process takes a very long time and can consequently become uneconomic if a large layer thickness of more than 1 μm is intended to be produced.
If dielectric layers are applied on structured metal planes, a good edge coverage of the metal layer is intended to be achieved. If thick metallizations are covered with a high metal proportion, cavities, so-called voids, can occur in the dielectric material, which significantly impair the properties of the component.
In the case of surface wave components provided with electrodes which are embodied in strip-type fashion and are intermeshed with one another in a comb-like manner, an undesirable material transport can occur, brought about by mechanical stress in the electrode material. Such a material transport takes place in the case of specific metallizations (for example composed of copper), principally at outer interfaces, for which reason it is necessary for the electrodes to be enveloped. A sufficiently good coverage of the outer interfaces of the electrodes cannot always be achieved in the desired manner, however, with the deposition methods mentioned.
In the case of bulk acoustic wave resonators, homogeneous dielectric layers are applied in order to alter the acoustic properties of a piezoelectric layer, that is, for example, altering and adapting the frequency of the resonator. Trimming processes can then be carried out at these dielectric layers in order to improve the frequency accuracy and the operating properties of the microacoustic components. Otherwise those components which do not comply with the predefined tolerance limits are separated out.
The adhesion of the layers produced by vapor deposition or sputtering in particular of hard layers, is inadequate under certain circumstances. If appropriate, it is necessary to reduce the layer thickness or, with additional outlay, to improve the surface area to which the layer is intended to be applied, for example in an O2 plasma.
German patent document 10 2008 016613 B4 describes a method for producing an electrical component comprising at least one dielectric layer on a substrate composed of piezoelectric material.